This invention relates to inkjet printers and, in particular, to systems and methods for processing ink.
Many types of printers are widely used today. One of the major types is the inkjet printer. An inkjet printer is a type of non-impact printer that forms images by controllably spraying drops of ink from a print head. Often the print head is part of a mobile print carriage that can traverse a given axis within the printer. It is common for inkjet printers to have more than one print head, especially color printers. Commonly, color inkjet printers have print heads containing various colors of ink including black ink. Each print head contains nozzles through which ink drops are ejected. The print nozzles eject or shoot ink drops across a small air gap onto a print media. Various inkjet printers are described in the following references: U.S. Pat. Nos. 6,234,613, 6,227,640, 6,193,345, and 6,179,414.
Several types of inkjet printers exist. One common type is a thermal inkjet printer. A processor of the thermal inkjet printer can apply a driving voltage to a thermal resistor contained in a nozzle. The driving voltage heats the resistor and indirectly the surrounding ink. This increased temperature results in increased pressure within the nozzle. The pressure causes some of the ink to be ejected from the nozzle in the form of drops or droplets. The thermal resistors are commonly formed on a single silicon wafer chip mounted in the print head. Exemplary printers are described in the following references U.S. Pat. Nos. 6,183,078, and 6,070,969. Another common type of inkjet printer uses piezo-electric crystals to force ink drops from the print nozzle in response to a signal.
Whatever control mechanism is used, the print nozzles are generally arranged in a print head and are oriented to shoot their ink in a desired direction from the print head towards the print media. However, it is not uncommon for print nozzles to become misaligned during assembly or to later become misaligned through use or transport. Any misalignment degrades the quality of the product produced by the printer since some of the drops end up in unintended locations on the print media. Specifically, this can cause blurring and other quality control problems. Print nozzles can also become clogged and stop functioning, further detracting from print image quality.
Attempts have been made to sense whether print nozzles are firing or not. However, these technologies require that the ink droplet physically contact the sensor thereby making it impossible to monitor for ink droplets while the printer is actually printing. Further attempts have been made to monitor the size and location of ink droplets using photo detectors. However, this technology is prone to failure due to contamination of the detector by ink particles. For references that discuss aspects of ink droplet detectors, the reader is referred to the following references: U.S. Pat. Nos. 6,227,644, and 6,086,190.
Accordingly, the present invention arose from concerns associated with providing improved image quality in inkjet printers by reducing degradation caused by print nozzle misalignment and malfunction.
Methods and systems for detecting ink droplets ejected by a printing device, and for determining whether the trajectory of the ink droplet deviates from a desired trajectory are described. One embodiment comprises an ink droplet trajectory detector which has multiple electrically conductive, electrically isolated sensors. At least one structure orients the sensors relative to one another. Each sensor can generate an electrical signal when an ink droplet passes in proximity to it. The sensors can generate a signal without an ink droplet physically engaging any portion of the sensors. Sensor-generated signals can then be processed to ascertain ink droplet trajectories.
In another embodiment, the ink droplet trajectory detector comprises an open-ended structure having multiple joined sides that define a passageway. Ink droplets can pass through the passageway. Multiple sensors are supported by the structure, with each side of the structure supporting at least one sensor. The sensors can generate signals when an ink droplet passes in proximity thereto. Sensor-generated signals can then be processed to ascertain ink droplet trajectories.
In a further embodiment, a method for determining a trajectory of an ink droplet comprises providing a sensor structure that can sense trajectories of ink droplets without physically contacting the ink droplets. An ink droplet is ejected from a print nozzle along a path that extends through the sensor structure. Multiple signals are produced from the structure upon passage of an ink droplet through the sensor structure. The signals can be processed to ascertain ink droplet trajectories.